Grafting of Monocarboxylic Substituted Polychlorotriphenylmethyl Radicals onto a COOH-Functionalized Self-Assembled Monolayer through Copper (II) Metal Ions O. Shekhah, † N. Roques, ‡ V. Mugnaini, ‡ C. Munuera, ‡ C. Ocal, ‡ J. Veciana,* ,‡ and C. Wo ¨ll* ,† Ruhr-UniVersita ¨t Bochum, Institut fu ¨r Physikalische Chemie 1, UniVersita ¨tsstrasse 50, D-44801 Bochum, Germany, and Institut de Cie `ncia de Materials de Barcelona (CSIC)-CIBER/BBN, Campus UniVersitari de Bellaterra, E-08193 Cerdanyola, Spain ReceiVed March 11, 2008 A monocarboxylic substituted polychlorotriphenylmethyl radical (PTMCOOH) has been grafted onto a COOH- functionalized SAM (mercaptohexadecanoic acid, MHDA SAM), using copper (II) metal ions as linkers between the carboxyl groups of the SAM and the ligand. The metal-radical adlayer has been characterized thoroughly using different surface analysis techniques, such as contact angle, IRRAS, XPS, SPR, ToF-SIMS, SFM, and NEXAFS. The magnetic character was confirmed by EPR. The density of unoccupied states was investigated using X-ray absorption spectroscopy. A low-energy peak in the NEXAFS spectrum directly revealed the presence of partially occupied electronic levels, thus proving the open-shell character of the grafted ligands. SEM measurements on a laterally patterned sample prepared by μCP of MHDA in a matrix of hexadecane thiolate (a CH 3 -terminated SAM) was performed to demonstrate that the metal-assisted anchoring of the open-shell ligand occurs selectively on the COOH terminated SAM. These results represent an easy and new approach to anchor organic radicals on surfaces and constitute a first step toward the growth of magnetic metal-organic radical-based frameworks on solid substrates. Introduction To control the organization of nano-objects on surfaces represents one of the main challenges in the field of nanotech- nology. To date, one of the most widely used approaches to manipulate a surface coverage is the use of self-assembled monolayers (SAMs) 1 composed of laterally organized molecules whose ending group confers relevant physical properties to the substrate. 2 These materials hold considerable potential in the field of molecular electronics and optoelectronics, as well as sensors. Nevertheless, the preparation of functional molecules substituted with the appropriate reactive group to bind the substrate often requires fine synthetic chemistry work, which constitutes, together with the unpredictable self-assembly behavior of these functionalized molecules, the main drawback of this approach. Another particularly appealing strategy to reach the same objective deals with the use of well-known SAMs that are formed with basic molecules. In this approach, the ending groups of the homogeneous and well-packed monolayer are used to graft the functional molecule to the surface thanks to covalent bonds or electrostatic interactions. To date, SAMs functionalized with suitable ending groups have been widely used to graft single molecule magnets (SMMs), 3 to construct molecular metal-or- ganic nanowires on top of electrodes, 4 or even to build porous coordination polymers. 5,6 Recently, a feasible approach was demonstrated to form one of the few examples of molecular magnetically active surfaces, 7 a fundamental starting point toward advanced nanodevices for magnetic data storage. In that work, a carboxylic-substituted polychlorotriphenylmethyl radical (PT- MCOOH, Figure 1) was grafted to a SAM functionalized with suitable ending groups, thanks to covalent and electrostatic interactions. These radical molecules not only allowed conferring a magnetic nature to the surface, but also a multifunctional character, thanks to their relevant electrochemical and optical properties. † Ruhr-Universita ¨t Bochum, Institut fu ¨r Physikalische Chemie 1, Uni- versita ¨tsstrasse 50, D-44801 Bochum, Germany. ‡ Institut de Cie `ncia de Materials de Barcelona (CSIC), Campus Universitari de Bellaterra, E-08193 Cerdanyola, Spain. (1) Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R. G.; Whitesides, G. M. Chem. ReV. 2005, 105, 1103. (2) (a) Matsushita, M. M.; Ozaki, N.; Sugawara, T.; Nakamura, F.; Hara, M. Chem. Lett. 2002, 596. (b) Areephong, J.; Browne, W. R.; Katsonis, N.; Feringa, B. L. Chem. Commun. 2006, 3930. (c) Namiki, K.; Sakamoto, A.; Murata, M.; Kume, S.; Nishihara, H. Chem. Commun. 2007, 4650. (d) Mannini, M.; Sorace, L.; Gorini, L.; Piras, F. M.; Caneschi, A.; Magnani, A.; Menichetti, S.; Gatteschi, D. Langmuir 2007, 23, 2389. (e) Cornia, A.; Fabretti, A. C.; Pacchioni, M.; Zobbi, L.; Bonacchi, D.; Caneschi, A.; Biagi, R.; Del Pennino, U.; De Renzi, V.; Gurevich, L.; Van der Zant, H. S. J. Angew. Chem., Int. Ed. 2003, 42, 1645. (3) (a) Zobbi, L.; Mannini, M.; Pacchioni, M.; Chastanet, G.; Bonacchi, D.; Zanardi, C.; Biagi, R.; Del Pennino, U.; Gatteschi, D.; Cornia, A.; Sessoli, R. Chem. Commun. 2005, 1640. (b) Gomez-Segura, J.; Ruiz-Molina, D.; Veciana, J. Chem. Commun. 2007, 3699. (4) Lin, C.; Kagan, C. R. J. Am. Chem. Soc. 2003, 125, 336. (5) (a) Hermes, S.; Schro ¨der, F.; Chelmowski, R.; Wo ¨ll, C.; Fischer, R. A. J. Am. Chem. Soc. 2005, 127, 13744. (b) Biemmi, E.; Scherb, C.; Bein, T. J. Am. Chem. Soc. 2007, 129, 8054. (6) (a) Shekhah, O.; Wang, H.; Strunskus, T.; Cyganik, P.; Zacher, D.; Fischer, R.; Wo ¨ll, C. Langmuir 2007, 23, 7440. (b) Shekhah, O.; Wang, H.; Kowarik, S.; Schreiber, F.; Paulus, M.; Tolan, M.; Sternemann, C.; Evers, F.; Zacher, D.; Fischer, R. A.; Wo ¨ll, C. J. Am. Chem. Soc. 2007, 129, 15118. (7) (a) Crivillers, N.; Mas-Torrent, M.; Perruchas, S.; Roques, N.; Vidal- Gancedo, J.; Veciana, J.; Rovira, C.; Basabe-Desmonts, L.; Ravoo, B. J.; Gergo- Calama, M.; Reinhoudt, D. N. Angew. Chem., Int. Ed. 2007, 46, 2215. (b) Crivillers, N.; Mas-Torrent, M.; Vidal-Gancedo, J.; Veciana, J.; Rovira, C. J. Am. Chem. Soc. 2008, 130, 5499. Figure 1. Chemical structure for the PTMCOOH radical. A Langmuir XXXX, xx, 000-000 10.1021/la800771q CCC: $40.75  XXXX American Chemical Society Published on Web 06/04/2008